Portable precision drill

ABSTRACT

A drill incorporates an axial feed drive, measuring system for determining the feed distance, a computer for controlling the axial feed drive as a function of the axial feed distance and a rotary drive for driving the tool spindle with pre-established on-load speed or pre-established torque or load moment. The flow or feed of cutting lubricant to the tool is controlled as a function of the pre-established on-load speed or the combination of the pre-established load moment, and the axial feed.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of portable drillsand more particularly to a portable drill for fastening onto thedrilling location of large workpieces for precision drilling work bymeans of a tool through which a liquid lubricant is conducted to thetool cutting edges, having a tool spindle which is displaceable in itsaxial direction by a separate drive with a tool holder, through whichthe lubricant is fed and a drive for the rotating axial advance of thetool spindle.

Such a drill is used in all precision drilling work in which theworkpieces are of such a size that they cannot be drilled on stationarydrilling machines. A preferred field of use of such drills is in theaeronautical industry in order, for instance, to produce, in airplaneconstruction, those holes which are to be provided for the attachmentbetween the fuselage and the wings. The drill in question is eitherarranged fixed on an auxiliary device or, in variable use, is employedin locking bushings, in templates, or in similar holding devices.Particularly exact precision of machining on the part of such drills isrequired upon the reaming of previously produced holes, for whichpurpose conical reaming tools having a conical shoulder are used.

THE PRIOR ART

The prior art related to drills including the drill shown in U.S. Pat.No. 4,688,970. U.S. Pat. No. 4,688,970 shows a drill which has a drivemotor which assures the feeding of the work spindle towards theworkpiece and back from it. Sensors are seated on the tool spindle inorder to check that the drill complies with the working data determinedover the working path, and in particular reaches the predetermined depthof drilling with the tool in order then to be withdrawn again from theborehole. Auxiliary means for detecting the top side of the workpiece inorder to be able to determine the depth of penetration of the tool intothe workpiece from that point are not present in the known apparatus.This is true also of other previously known drills which have only asingle drive, both for the rotating of the tool spindle and for thefeeding thereof. In these machines, when they are under load, the feeddecreases also simultaneously with the speed of rotation; on the otherhand, the basic speed of rotation upon idle travel must not be selectedtoo high, so that the idle distances here can be moved over only withrelatively low speed.

One essential disadvantage of the known drill machine lies in its highconsumption of lubricant, this being a drilling liquid of high qualitywhich is very expensive. The amount of lubricant fed is establishedempirically based on an estimate of the drilling or reaming process,regardless of the length of engagement of the tool. The drilling orreaming tools used for precision holes have, distributed over theirentire cutting length, radial holes which are supplied from a centralfeed channel. Since the cutting agent is fed continuously in the knownembodiments, overdosing takes place as long as the tool is not inengagement over its entire cutting length. Also upon the pulling back ofthe tool without drilling or reaming work, the lubricant continues to befed, unutilized, in the known drills. As a whole, therefore, theconsumption of lubricant is about ten times as high as required from apurely theoretical standpoint for the actual cutting process.

The known drills also have disadvantages structurally. The tool spindleis mounted at the rear of the machine in an axial conveying thread whichis necessary for the feed. Despite additional supporting of the spindlein the front region of the machine, movements of radial deflection areunavoidable, which impairs the accuracy of the drilling. Furthermore,the machining distance, the drilling depth, cannot be preciselydetermined in the known machines since for this, a depth stop isrequired which is placed on the wall of the material surrounding thehole in question and which indicates that the drilling depth has beenreached in the manner that the tool spindle comes against acorresponding stop on the inner end of the depth stop, as a result ofwhich the feed is turned off.

Finally, the known drilling machines are complicated to adjust. Eachtool is subject to wear and must be regularly replaced, must have itsworking stroke readjusted empirically in a testing shop. This is done byturning the tool spindles together with their aforementioned conveyorscrew in and out of the corresponding threaded bushing for the feed, forwhich a partial assembling of the machine, at least in the front regionof the mechanical drive, is necessary in order to be able axially todisplace a setting or stop nut on the conveyor thread of the toolspindle which strikes against the inner end of the depth stop at the endof the working stroke.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a portable precisiondrill which operates with a high degree of precision and is economicalin the consumption of lubricant.

The foregoing and other objects and advantages of the present inventionwill appear more clearly hereinafter.

In accordance with the present invention there is provided a portableprecision drill which incorporates a measuring system for determiningthe feed distance, a computer for controlling the feed drive as afunction of the axial feed distance and a rotary drive for driving thetool spindle with pre-established on-load speed or pre-establishedtorque or load moment. The flow or feed of lubricant to the tool iscontrolled as a function of the pre-established on-load speed or thecombination of the pre-established load moment, and the feed.

It is essential for the invention to be able to operate the motor forthe rotary drive always at full load either with the highest possiblespeed of rotation or with the greatest possible torque. It is optimal toadapt these operating parameters to the drilling output and therefore towork with the greatest possible drilling output. The separate feeddrive, the feed speed of which is independent of the speed of rotationof the rotary drive, can be operated with a high feed speed at the startof the machining cycle when the tool is not yet in engagement with thematerial or only slightly in engagement with it, after which, as afunction of the decrease in the speed of rotation of the rotary drivemotor, the feed speed is reduced in accordance with a pre-establishedfunction. This control or regulation can also be effected as a functionof the torque, which is dependent on the specific operating conditions,such as, for instance, the characteristics of the material. Suitablesensors for speed of rotation and/or torque are installed in the rotarydrive and the suitable desired value to be set in each case can bederived in suitable manner so as to introduce it into the computer andevaluate it there.

As a result of the evaluation in the computer, the feed of the liquidlubricant is also controlled so that the smallest possible amount oflubricant is used. Thus, at the start of the machining process as longas the tool is only slightly in engagement with the material, only asmall amount of lubricant is fed and the addition of lubricant isincreased with increasing machining engagement.

The separation of rotary drive from feed drive affords the furtheradvantage that towards the end of the drilling or reaming process, onecan operate with only a slight feed, which greatly increases theprecision of the machining upon full engagement of the tool. For this,there is necessary an exact determination of the instantaneous positionof the tool, for which the measurement system for determining the feeddistance serves. As a function of a reference point, the position at thetime of the tool spindle in axial direction is determined, for which aso-called absolute distance measurement is provided. To this distancemeasurement system there is connected a sensor system which is placed onthe surface of the workpiece to be machined in the direct vicinity ofthe tool engagement and establishes a reference point. Furthermore, thedata of the specific tool employed can be entered into the computer ofthe apparatus and in this way the working stroke which enters intoconsideration in each case can be fixed so that up to the end of thefine drilling one can work precisely with the slight feed.

The measurement system for the feed distance makes it possiblefurthermore to operate with the highest possible feed of the separatelydeveloped feed drive until engagement of the tool, which considerablyshortens the entire machining time so that the machining cycle requiresonly about one-third as much time as traditional machines.

The measurement system for determination of the feed distance makes itpossible furthermore to establish the maximum wear of the tool in themanner that, for instance, comparative values are stored in the computerand the deviation from these reference values determined. Furthermore,the determination of the feed or working distance of the tool createsthe possibility of temporarily withdrawing the tool even during themachining process so that, fort instance, problematic chips can beremoved from the borehole.

The computer of the drilling machine serves for the evaluating of alldata and for controlling the functions and operations. Furthermore,there is provided on the drilling machine a memory chip which bears theindividual data of the machine and of the tool used, which areintroduced upon overhaul or upon new use of the apparatus. At thebeginning of each use, these data are interrogated and fed to thecomputer, evaluated in it so that the working distance and the lubricantfeed can be determined. In this way, the maintenance data of the drilland of the tool can be pre-established so that the maximum wear is notexceeded. Via a data interface, the drill can be linked with anotherdrill and/or a central computer so as to permit of central monitoringand evaluation of the operating data of the machines and tools.

DESCRIPTION OF THE DRAWINGS

Other important objects and advantages of the invention will be apparentfrom the following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic view, partially in longitudinal section, of aportable precision drill made in accordance with the present invention;

FIG. 2 is a view of the front region of the drill of FIG. 1, drawn to anenlarged scale;

FIG. 3 is a view of the rear region of the drill of FIG. 1, drawn to anenlarged scale; and

FIG. 4 is a diagrammatic view of the feeding of lubricant to the tool ofthe drill of FIG. 1, showing three different positions of the tool.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, wherein like reference numbers designatelike or corresponding parts throughout, there is shown in FIGS. 1-3 aportable precision drill 100 made in accordance with the presentinvention which includes a tool spindle 1 mounted in a machine frame102. The tool spindle 1 has a tool holder 2 at its front end. In itthere is inserted a drilling or reaming tool 3 which has an axialchannel 4 for the feeding of a lubricant to the tool cutting edges.Communicating the axial channel 4 there are transverse holes 5 which arearranged over the entire length of the cutting region of the tool 3. Thefeeding of the lubricant to the tool 3 takes place through the toolspindle 1 which, for this purpose, has an axial channel 6 which extendsfurther in axial direction up to the rear end of the drill 100.

In order to effect the advance of the tool 3 upon the machining process,the tool spindle 1 is mounted for displacement in its axial direction.For this there are provided two bushings 7 which are rotatably supportedin the machine frame 102 and have within them para-axial longitudinalgrooves in which balls 8 are arranged. Balls 8 engage in para-axiallongitudinal grooves 9 in the tool spindle 1 so that the tool spindle 1can turn with the rotatably mounted bushings 7 and, independentlythereof, be pushed in axial direction with respect to the bushings 7. Inorder to avoid radial play of the tool spindle 1 as far as possible, thebushings 7 are arranged at the greatest possible distance from eachother. Thus, in the withdrawn end position of the tool spindle 1, thetool holder 2 lies directly at the outlet end of the front bushing 7,referred to the direction of feed. In the same way, the rear end of thetool spindle 1 in the advanced end position lies directly at theentrance end of the rear bushing 7.

The tool spindle 1 is placed in rotation by a rotary drive 15 whichincludes a gear rim 10 which is seated on the outer circumferential sideof the front bushing 7. Via a toothed gearing 11 this gear rim 10 on thebushing 7 is in engagement with an output gear 12 of a motor 13 which isarranged para-axial to the tool spindle 1. The motor 13 can be acompressed-air motor which is of relatively high power but of smallsize.

The motor 13 is operated under load with a predetermined speed ofrotation so that the tool spindle 1 and thus the tool 3 are alsomaintained at a given speed of rotation. The motor 13 can thus beoperated in the most favorable power range, in which connection ititself need not be further controlled or regulated.

Rather, merely the speed of rotation of the rotary drive 15 is detected,for which purpose a speed measuring device 14 is seated at a suitableplace in the rotary drive 15. The speed-dependent signal of the speedmeasuring device 14 is introduced into a computer 104 which, on thebasis thereof, determines the feed speed for the tool spindle 1. Thecomputer 104 is illustrated schematically by the rectangle 106 inFIG. 1. The computer 104 is connected to the lubricant feed device 31and to the feed drive 25 by conventional connections. As long as thespeed of rotation of the rotary drive 15 for instance at the start of amachine cycle has still not dropped to the optimal on-load speed, onecan operate with an increased feed, which is completely uncoupledmechanically from the speed of rotation of the rotary drive 15. Insteadof a compressed-air motor there can also be used as motor 13 an electricmotor which, in addition, affords the possibility of being operated witha predetermined load moment, which can be determined via the currentconsumption of the electric motor.

The computer 104 controls a feed drive 25 in the manner that upon theidle travel over which the tool 3 is not in engagement with thematerial, one can operate with maximum speed of feed, which is true bothfor the start of an operating cycle and for the extracting of the tool.Furthermore, the feed drive 25 is so regulated that optimal cuttingconditions with due consideration of the most favorable on-load speed ofthe motor 13 are maintained. In this connection furthermore, adistinction is made between normal machining and precision machining,high speed of rotation and low feed being used in the latter case.

As shown in FIGS. 1 and 3, the feed drive 25 comprises a rotatablymounted threaded spindle 17 which is not displaceable in axialdirection. The threaded spindle 17 engages into a hollow section 16 inthe region of the rear end of the tool spindle 1. On the threadedspindle 17 a nut 18 is arranged in such a manner that it is fixed indirection of rotation, this being assured by a carriage 20 which isguided on a para-axial guide 21 on the machine frame. This guide 21extends over a region of axial displacement of the nut 18 whichcoincides with the total feed distance of the tool spindle 1. The rearend of the hollow section 16 of the tool spindle 1 is rotatablysupported in the nut 18, but is firmly attached in axial direction withthe displaceable nut 18. By means of rotary balls 19 which engage bothin the threaded spindle 17 and in a mating thread of the nut 18, theaxial displacement of the nut 18 and thus the feed of the tool spindle 1are effected upon rotation of the threaded spindle 17. The rotary driveof the threaded spindle 17 is effected via a belt transmission 22 bymeans of a feed motor 23, which can be a stepping motor.

The belt drive 22 furthermore drives a measurement system 24 whichconsists predominantly of an incremental rotary transducer. Via thesignals supplied by the rotary transducer, the feed distance of the toolspindle 1 can be precisely determined so that an absolute measurement ofthe distance is possible. The measurement system 24 is connected incorresponding manner with the computer 104 or the drill machine 100, soas to control the feed of the tool 3 for the predeterminable idledistances as well as the machining and precision machining distances viathe feed drive 25 and possibly readjust it as a function of the speed ofrotation of the tool spindle 1 which can be detected via the speed ofrotation measuring device 14.

As further shown in FIG. 1, the measurement system 24 can besupplemented for the detection of the feed distance by means of a depthsensor which is connected by a rod 29 to a feeler tube 27 which isarranged in a sleeve 26 which surrounds the tool 3 in its withdrawn endposition. The feeler tube 27 also surrounds the tool 3 and has a feelernose 28 which can be placed on the material of the workpiece in questionin the region of the edge of the hole to be machined. Since the distancebetween the tool and the feeler end of the feeler nose in its fullyextended position is known, a reference signal for the tool spacing inthe initial position can be determined via the feeler sensor 30 via thedistance of indentation of the seated feeler nose 28 when the drill isplaced on a workpiece. In particular, in this way it is possible toestablish a zero point for the control or regulating of the computer 104in cooperation with the measurement system 24.

From FIG. 1 it can furthermore be noted that the axial channel 6 for thefeeding of the lubricant to the tool 3 extends not only through the toolspindle 1 but also through the threaded spindle 17 up to a lubricantfeed device 31 which is placed on the rear end of the drill 100. In theaxial channel 6 a lance 32 in the form of a small tube is present, ascan be noted in detail from FIG. 4. The lubricant is transported throughthis lance 32 from the lubricant feed device 31 to the tool 3 in such amanner that it emerges there through the corresponding transverse holes5 which adjoin the lubricant channel 4 of the tool 3 only when it isalso actually used. This is the case upon engagement by the tool 3 withthe material of workpiece but not upon the empty paths which the tool 3has moved over at the start of an operating cycle and upon thewithdrawal from the hole drilled. When the tool 3 is withdrawn, thelance 32 extends so far into the lubricant channel 4 of the tool thatall the transverse holes 5 are closed. Over the first idle path whichthe tool must move over up to the borehole, the lance 32 travels alongso as to keep all the transverse holes 5 closed, as previously. For thispurpose, the lance 32 is held displaceable by the distance "X" in axialdirection in the lubricant feed device 31, in which connection it ispressed by means of a rear spring 33 in the direction towards the toolholder 2 of the tool spindle 1. When the lance 32 has reached in feeddirection the end of the axial displacement path, a relative movementtakes place between the lance 32 and the tool 3 upon the further feedingof the tool 3, in the manner that, starting with the front transversehole 5, the transverse holes 5 are gradually unblocked for the emergenceof the lubricant. Upon the pulling out of the tool 3, the transverseholes 5 are closed in the reverse sequence, and the relative movementbetween the tool 3 and the lance 32 ends as soon as the lance 32 isseated at the front end of the axial lubricating channel 4 of the tool3. Instead of this, there can also be provided a different drivingdevice 34 in order to effect the pushing back of the lance 32 into thestarting position.

The computer 104 of the drill 100 also controls the lubricant feeddevice 31 since the need for lubricant is not only dependent on thedistance but must also be adapted to the specific operating conditions,such as the main machining process or the precision m machining. Thelubricant feed device 31 conveys the lubricant in portions into thelance 32, in which connection air bubbles between the individualportions of lubricant are forced into the lance 32. In this way, thelubricant is atomized upon emergence from the transverse holes 5 of thetool 3, assuring a uniform wetting of the cutting places. Furthermore,the lubricant feed device 31 can be operated in a variable pulse-pauseratio, in which case, for the duration of the pulse, either onlylubricant or portions of lubricant with air bubbles are introduced intothe lance 32, while for the duration of the pauses, only air isintroduced into the lance 32. In particular, in this way one can avoidthe possibility that a residual volume of lubricant which is stillpresent in the entire lubricant feed line is discharged out of thetransverse holes upon the pulling back of the tool 3.

The computer 104 performs an evaluation of all data and controls thefunctions and operations of the drill 1. Furthermore, there is providedin the computer 104 a memory chip which bears the individual data of thedrill machine 1 and of the tool 3 used, which are introduced uponoverhaul or upon new use of the apparatus 1. At the beginning of eachuse, these data are interrogated and fed to the computer 104, evaluatedin it so that the working distance and the lubricant feed can bedetermined. In this way, the maintenance data of the drill 1 and of thetool 3 can be pre-established so that the maximum wear is not exceeded.Via a data interface, the drill 1 can be linked with another drill 1and/or a central computer so as to permit of central monitoring andevaluation of the operating data of the machines and tools 3.

The foregoing specific embodiments of the present invention as set forthin the specification herein are for illustrative purposes only. Variousdeviations and modifications can be made within the spirit and scope ofthis invention, without departing from the main theme thereof.

I claim:
 1. A portable drill for performing drill operations on aworkpiece comprising:a frame; a tool spindle displaceably mounted onsaid frame; feed drive means mounted on said frame and connected to saidtool spindle for displacement of said tool spindle; rotary drive meansfor rotation of said tool spindle; measurement system means mounted onsaid frame; depth sensor means mounted on said measurement system meansfor detecting feed distance of said tool spindle; computer means mountedon said frame for regulating said feed drive means with said computermeans connected to said rotary drive means and to said feed drive meansfor the purpose of regulating said feed drive means as a function ofdecrease in speed of said rotary drive means during operation with adecrease in said feed drive speed corresponding to a decrease in saidrotary drive speed; axially displaceable feeler nose means disposedgenerally para-axially with respect to said tool spindle for the purposeof making contact with said workpiece for detecting a reference portionof said workpiece; and lubricant feeding means mounted on said frame forfeeding lubricant as a function of said rotary drive speed.
 2. A drillaccording to claim 1, further comprising:tool spindle mounting means formounting said tool spindle in said frame with said tool spindle mountingmeans comprising: a rotatable bushing connected to said rotary drivemeans; a groove member of said tool spindle with said groove memberhaving a plurality of generally para-axial grooves; a groove member ofsaid rotary drive means, with said groove member having a plurality ofgenerally para-axial grooves; and a plurality of balls, with said ballsengaging said groove member of said rotary drive means and said toolspindle thereby forming a driving connection.
 3. A drill according toclaim 2, wherein said tool spindle mounting means comprises:a firstbushing and a second bushing, with said first bushing spaced apart fromsaid second bushing and with said tool spindle having a first end and asecond end and with said tool spindle capable of an extended positionand a retracted position, with said first and said second bushing spacedapart to support said tool spindle when said tool spindle is in saidextended position and in said retracted position.
 4. A drill accordingto claim 1, wherein said rotary drive means comprises a motor, with saidmotor disposed generally paraxially relative to said tool spindlemounting means and disposed generally proximate to said tool spindlemounting means.
 5. A drill according to claim 1, further comprising:aspeed indicator disposed on said rotary drive means.
 6. A drillaccording to claim 1, wherein said feed drive means comprises:arotatably mounted threaded spindle; a nut, with said nut threaded ontosaid threaded spindle with said, nut fixed in the direction of rotationand displaceable in axial direction along said threaded spindle, withsaid nut connected to said tool spindle.
 7. A drill according to claim6, wherein said tool spindle comprises:a hollow section, with saidthreaded spindle projecting into said hollow section and with said nutaxially disposed on said tool spindle.
 8. A drill according to claim 6,further comprising:a feed motor, with said feed motor connected to saidthreaded spindle; and incremental rotary transducer means with saidincremented rotary transducer means connected to said threaded spindlefor measurement of feed distance of said tool spindle.
 9. A drillaccording to claim 8, wherein said feed motor and said incrementalrotary transducer means are disposed on said tool spindle generallydiametrically opposite said rotary drive means.
 10. A drill according toclaim 1, comprising:an axial channel portion formed in said tool holder,and an axial channel portion formed in said tool spindle with saidchannel portion in said tool holder communicating with said channelportions in said tool spindle for feeding of lubricant; said lubricantfeed means mounted on said tool spindle and communicating with saidchannel portion in said tool spindle for feeding lubricant through saidchannel portion in said tool spindle and through said channel portion insaid tool holder.
 11. A drill according to claim 10, furthercomprising:a hollow tool mounted in said tool holder; a hollow lance,with said hollow tool having a plurality of transverse hole portions,and with said hollow lance disposed projecting into said hollow tool andprojecting into said axial channel portion formed in said tool spindle.12. A drill according to claim 11, wherein said hollow tool has awithdrawn position and an extended position and in which said lance isof such a length so that when said hollow tool is in said withdrawnposition, said transverse hole portions are blocked, and as said hollowtool advances toward said extended position, said transverse holeportions gradually open.
 13. A drill according to claim 11, furthercomprising:said lubricant feed means disposed to feed lubricant intosaid hollow lance.
 14. A drill according to claim 10, in which saidlubricant feed means is disposed to feed lubricant into said axialchannel portion in said tool spindle intermittently with air bubblesintroduced between portions of lubricant.
 15. A drill according to claim11, wherein said lubricant feed means is disposed to introduce lubricantinto said hollow lance intermittently with air bubbles introducedbetween portions of lubricant.
 16. A drill according to claim 10,further comprising:said computer means connected to said lubricant feedmeans, with said computer means capable of a variable pulse-pause ratiooperation defined as directing the flow of only lubricant or lubricantwith air bubbles into said hollow lance during pulse operation anddirecting the flow of only air into said hollow lance during pauseoperation.
 17. A portable drill for performing drill operations on aworkpiece comprising:a frame; a tool spindle displaceably mounted onsaid frame; feed drive means mounted on said frame and connected to saidtool spindle for displacement of said tool spindle; rotary drive meansfor rotation of said tool spindle; measurement system means mounted onsaid frame; depth sensor means mounted on said measurement system meansfor detecting feed distance of said tool spindle; computer means mountedon said frame for regulating said feed drive means, with said computermeans connected to said rotary drive means and to said feed drive meansfor the purpose of regulating said feed drive means as a function ofdecrease in speed of said rotary drive means during operation, with adecrease in said feed drive speed corresponding to a decrease in saidrotary drive speed; axially displaceable feeler nose means disposedgenerally para-axially with respect to said tool spindle for the purposeof making contact with said workpiece for detecting a reference portionof said workpiece; and lubricant feeding means mounted on said frame forfeeding lubricant as a function of load moment and feed distance.
 18. Adrill according to claim 1, wherein said rotary drive means comprisesmotor means and further comprising:speed indicator means disposed onsaid motor means.
 19. A drill according to claim 11, furthercomprising:said lubricant feed means disposed to feed lubricant intosaid axial channel portion in said tool spindle.
 20. A drill accordingto claim 11 further comprising:spring means, with said spring meansdisposed to urge said lance in a feed direction relative to said tool.